Process for the preparation of a microspheroidal catalyst

ABSTRACT

Process for preparing a catalyst active for the fluid bed acetoxylation of ethylene to produce vinyl acetate. The process comprises the steps of (a) impregnating microspheroidal silica support particles by the incipient wetness technique with an aqueous solution of palladium and gold compounds, whilst agitating the support particles; (b) drying the impregnated support particles produced in step (a) whilst agitating the impregnated support particles; (c) reducing the palladium and gold compounds of the impregnated support particles produced in step (b) to respective metals by adding the dried, impregnated support particles to an aqueous solution of hydrazine, whilst stirring, to form a slurry; (d) filtration of the slurry produced in step (c) to remove the excess reduction solution; (e) washing the filter cake/slurry produced in step (d) with water and removing excess water to form a cake; (f) impregnating the cake produced in step (e) with one or more salts of Group I, Group II, lanthanide and transition metals by blending the cake produced in step (e) with one or more solid salts of Group I, Group II, lanthanide and transition metals; and (g) drying the impregnated cake produced in step (f) whilst agitating the impregnated cake to form free-flowing catalyst particles.

This application is the U.S. National Phase of International ApplicationPCT/GB02/5761, filed 18 Dec. 2002, which designated the U.S.

The present invention relates to a process for preparing a catalystactive for the fluid bed acetoxylation of ethylene to produce vinylacetate and to generally applicable aspects of such a process.

BACKGROUND OF THE INVENTION

The process for preparing catalysts active for the acetoxylation ofethylene to produce vinyl acetate are known for example from Europeanpatent publication EP-A-0672453 which relates to a process for thepreparation of a fluid bed catalyst comprising impregnating a supportcomprising a mixture of substantially inert microspheroidal particleswith a solution comprising salts of palladium and a metal M selectedfrom the group consisting of barium, gold, lanthanum, niobium, cerium,zirconium, lead, calcium, strontium, antimony and mixtures thereof.EP-A-0672453 describes preparation processes in which metal saltcompounds are reduced using hydrazine.

Several processes are described for the treatment of hydrazinecontaining aqueous streams. These involve decomposition of hydrazinewith an oxidising agent in the presence of a noble metal or base metalcatalyst (e.g. JP 2000107774, JP 63205194, JP 63036894). This oxidativedecomposition may also be performed in the presence of alkali (e.g. JP63049295). In the absence of an oxidant hydrazine is readily decomposedeither thermally or in the presence of a catalyst to nitrogen and/orammonia.

DESCRIPTION OF THE INVENTION

Processes for the preparation of catalysts for the fixed bed productionof vinyl acetate are well established and described in the patent andscientific literature. There remains a need for an improved process forthe commercial scale preparation of a catalyst active for the fluid bedacetoxylation of ethylene to produce vinyl acetate. This inventionprovides an integrated process for the production of a fluid bedcatalyst for this process.

According to one aspect of the present invention there is provided aprocess for preparing a catalyst active for the fluid bed acetoxylationof ethylene to produce vinyl acetate, which process comprises the stepsof:

-   -   (a) impregnating microspheroidal silica support particles by the        incipient wetness technique with an aqueous solution of        palladium and gold compounds, whilst agitating, preferably        continuously agitating, the support particles;    -   (b) drying the impregnated support particles produced in        step (a) whilst agitating the impregnated support particles;    -   (c) reducing the palladium and gold compounds of the impregnated        support particles produced in step (b) to respective metals by        adding the dried, impregnated support particles to an aqueous        solution of hydrazine, whilst stirring, to form a slurry;    -   (d) filtration of the slurry produced in step (c) to remove the        excess reduction solution;    -   (e) washing the filter cake/slurry produced in step (d) with        water and removing excess water to form a cake;    -   (f) impregnating the cake produced in step (e) with one or more        salts of Group I, Group II, lanthanide and transition metals by        blending the cake produced in step (e) with one or more solid        salts of Group I, Group II, lanthanide and transition metals;        and    -   (g) drying the impregnated cake produced in step (f) whilst        agitating the impregnated cake to form free-flowing catalyst        particles.

The present invention provides a process which is integrated and hasseveral advantages that are particularly suited to the production of amicrospheroidal catalyst.

Thus, impregnation of the microspheroidal particles by the incipientwetness technique whilst agitating the support has been found to be aneffective way of providing relatively uniform impregnation. By use of avessel capable of being heated and agitated simultaneously,advantageously the subsequent drying stage can be performed using thesame apparatus. This has advantages of reducing the handling of thematerial and controlling the location and distribution of theimpregnated precursor metal salts.

Thus, according to a further embodiment of the present invention thereis provided a process for impregnating microspheroidal catalyst supportparticles with at least one compound of a catalytically active metal,which process comprises the steps of:

-   -   (a′) impregnating the microspheroidal support particles by the        incipient wetness technique with an aqueous solution of the at        least one catalytically active metal, whilst agitating the        support particles; and    -   (b′) drying the impregnated support particles produced in step        (a′) whilst agitating the impregnated support particles.

In the processes of the present invention, the microspheroidal supportparticles are suitably selected from the group consisting of inorganicoxides such as silica, alumina, zirconia and mixtures thereof,preferably silica. The microspheroidal support particles are preferablyresistant to attrition during agitation in the processes of the presentinvention.

Suitable support particles have a distribution of larger to smallerparticle sizes. Typically, at least 80% and preferably at least 90% ofthe support particles have mean diameters of less than about 300microns.

A typical catalyst useful in the present invention may have thefollowing particle size distribution:

0 to 20 microns  0–30 wt % 20 to 44 microns  0–60 wt % 44 to 88 microns10–80 wt % 88 to 106 microns  0–80 wt % >106 microns  0–40 wt % >300microns 0–5 wt %

Persons skilled in the art will recognize that support particles sizesof 44, 88, and 300 microns are arbitrary measures in that they are basedon standard sieve sizes. Particle sizes and particle size distributionsmay be measured by an automated laser device such as a Microtrac X100.

Microspheroidal support particles useful in the present invention aresufficiently porous to permit gaseous reactants to diffuse into theparticle and contact catalytic sites incorporated within the particle.Thus, the pore volume should be high enough to permit gaseous diffusion.However, a support particle with an exceedingly high pore volumetypically will not have sufficient attrition resistance or will not havesufficient surface area for catalytic activity. A typically suitablemicrospheroidal support particle has a pore volume (measured by nitrogensorption) between about 0.2 and 0.7 cc/g. A preferable support particlehas a pore volume between about 0.3 and 0.65 cc/g and more preferablybetween about 0.4 and 0.55 cc/g.

Surface areas (measured by nitrogen BET) for support particles with meandiameters and pore volumes useful in the present invention typically areabove about 50 m2/g and may range up to about 200 m2/g. A typicalmeasured surface area is about 60 to about 125 m2/g.

Typically useful support particles, especially silica support particlesare described in U.S. Pat. No. 5,591,688, incorporated by referenceherein. In these supports microspheroidal particles are produced byspray drying a mixture of a silica sol with silica particles followed bydrying and calcining. In the preparation, at least 10 wt. %, preferablyat least 50 wt. %, of a silica sol is mixed with particulate silica. Auseful particulate silica is a fumed silica such as Aerosil® (DegussaChemical Company). A typical silica particulate material has a highsurface area (about 200 m2/g) with essentially no micropores, and,typically, are aggregates (with mean diameters of several hundred nm) ofindividual particles with average diameters of about 10 nm (above 7 nm).Preferably, the silica is sodium free. Sufficient particulate silica isadded to the mixture to obtain a desired pore volume in the resultingsupport particle. The amount of particulate silica may range up to 90wt. % and typically ranges up to 10 to 50 wt. % of the silica in themixture. Typically, the silica sol/particulate silica mixture is spraydried at an elevated temperature such as between 115° to 280° C.,preferably 130° to 240° C., followed by calcining at temperaturetypically ranging from between 550° to 700° and, preferably 600° to 660°C.

An advantageous silica sol for preparing a catalyst support useful inthe present invention contains silica particles in the sol typicallymore than 20 nanometers in mean diameter and may be up to about 100nanometers or more. Preferable sols contain silica particles of about 40to 80 nanometers. Nalco silica sol 1060 particularly is advantageousbecause of the relatively large mean silica particle sizes of 60 nm packless efficiently than smaller sol particles such as Nalco 2327 at about20 nm. The larger particle size so yields a final support with highermesopore volume and less micropore volume.

In the processes of the present invention the particulate supportparticles are impregnated with at least one compound of a catalyticallyactive metal. Preferably, the catalytically active metal comprises atleast one Group VIII noble metal. The noble metals of Group VIII of thePeriodic Table of the Elements (IUPAC) are palladium, platinum, rhodium,ruthenium, osmium and iridium. Typically, the noble metal used in aprocess according to the present invention for preparing a catalystactive for the acetoxylation of ethylene to produce vinyl acetatecomprises palladium. Such a catalyst typically contains at least about0.1%, preferably at least 0.2 wt % palladium to about 5 wt % andpreferably up to 4 wt % palladium.

In the processes of the present invention the microspheroidal supportparticles are impregnated by the incipient wetness technique. In thistechnique the support is contacted with a solution of the compounds tobe impregnated in an amount which is from 60 to 120% of the pore volumeof the support particles, preferably from 70 to 100% of the pore volume.Suitable solvents may be water, carboxylic acids such as acetic acid,benzene, toluene, alcohols such as methanol or ethanol, nitrites such asacetonitrile or benzonitrile, tetrahydrofuran or chlorinated solventssuch as dichloromethane. Preferably, the solvent is water and/or aceticacid. Suitably, and especially when the present invention is used forthe preparation of a catalyst active for the acetoxylation of ethyleneto produce vinyl acetate, the support particles are impregnated withpalladium acetate, sulphate, nitrate, chloride or halogen-containingpalladium compounds such as H₂PdCl₄, which is sometimes also representedas [PdCl₂]2HCl, and Group I or Group II salts thereof such as Na₂PdCl₄and K₂PdCl₄. A preferred water soluble compound is Na₂PdCl₄. A preferredacetic acid-soluble palladium compound is palladium acetate. Thepalladium compounds may be prepared in situ from suitable reagents.

The catalyst active for the manufacture of vinyl acetate may alsocomprise, as promoters, other metals such as gold, copper, cerium andmixtures thereof, preferably gold. These promoters may be used in anamount of 0.1 to 10% by weight of each promoter metal present in thefinished catalyst composition. Typically, the weight percent of gold isat least about 0.1 wt %, preferably, at least 0.2 wt % gold to about 3wt % and preferably up to 2 wt % gold. Typically, the weight percent ofcerium is at least about 0.1 wt %, preferably at least 0.2 wt % to about10 wt % or more, preferably up to 5 wt % of cerium. Typically, theweight percent of copper is at least 0.1 to about 10 wt %, preferably upto 5 wt % copper.

Suitable gold compounds which may be used include gold chloride,dimethyl gold acetate, barium acetoaurate, gold acetate,tetrachloroauric acid (HAuCl₄, sometimes represented as AuCl₃.HCl) andGroup I and Group II salts of tetrachloroauric acid such as NaAuCl₄ andKAuCl₄. Preferably, the gold compound is HAuCl₄. The gold compounds maybe prepared in situ from suitable reagents.

The agitation of the support particles during the incipient wetnessimpregnation step and during the subsequent drying step may be performedin an agitated blender such as ribbon, ploughshare, V-type. This has anadvantage that the same apparatus may be used for both steps.

Preferably, the drying of impregnated particles is performed byagitating the support particles whilst applying external heat at atemperature in the range upto 150° C. This achieves rapid drying withoutredistribution of the metal complexes or precursor salts which has anadvantage of avoiding metal migration to give uniformly impregnatedmaterial.

Thus, according to a further aspect of the present invention, there isprovided a process for drying impregnated microspheroidal catalystsupport particles, which process comprises agitating the impregnatedsupport particles whilst applying external heat at a temperature in therange 50 to 200° C., preferably 100 to 150° C.

Dry gas such as air, nitrogen, at room temperature to 200° C. may bepassed over and/or through the catalysts during drying. After drying,the support particles impregnated with at least one compound of acatalytically active metal may be contacted with a reducing agent toconvert the compound to its respective metal.

Thus, according to yet a further aspect of the present invention thereis provided a process for reducing at least one compound of acatalytically active metal impregnated within microspheroidal supportparticles, to its respective metal, which process comprises adding theimpregnated microspheroidal support particles to a solution of areducing agent active for reduction of the at least one metal compoundto its respective metal whilst stirring.

It has been found that addition of the impregnated particles to asolution of a reducing agent rather than addition of the solution ofreducing agent to the impregnated support particles has benefits,especially for preparing catalyst active for the acetoxylation ofethylene to produce vinyl acetate in a fluid bed process. In particular,this aspect of the present invention provides a process in which thereducing agent is at a high concentration and excess relative to thecompound being reduced throughout the reaction. This has been found toproduce a layer structure, which is especially beneficial for preparinga catalyst active for the acetoxylation of vinyl acetate. In thislayered structure the support particles have at least one catalyticallyactive metal or precursor thereof distributed therein, in which themetal or precursor thereof is distributed in the support particle in alayer below the surface of said particle, said layer being between aninner and an outer region of said support particle, and each of saidinner and outer regions having a lower concentration of said metal orprecursor thereof than said layer. This provides an advantage in thatthe outer layer of the catalyst acts as a protective layer and serves toreduce the loss of metals upon attrition of the particle whilst stillmaintaining the activity of the catalyst. The outer region of thecatalyst composition may also provide some resistance to poisoning ofthe catalytically active metal.

Preferably the reducing agent active for the reduction of at least onemetal compound to its respective metal comprises hydrazine. Preferablythe solution of said reducing agent is an aqueous solution of hydrazine,more preferably an aqueous solution of hydrazine that has not beenrendered alkaline by an alkali metal hydroxide. Most preferably thesolution of said reducing agent consists of hydrazine in aqueoussolution in the absence of any other added components. It hassurprisingly been found that aqueous hydrazine is active for thereduction of at least one metal compound to its respective metal evenwhen not been rendered alkaline by an alkali metal hydroxide

Suitably, at least one compound impregnated in the support comprisespalladium and gold compounds and the reducing agent comprises hydrazinein aqueous solution.

Preferably, the concentration of hydrazine in the aqueous solution is 1to 20 wt %, such as 3 to 20 wt %, for example 5 to 20 wt %.

When hydrazine is used as reducing agent, excess hydrazine may be washedfrom the support material. During reduction with hydrazine it isbeneficial to pass an inert gas such as nitrogen over or through thesupport particles to remove oxygen (air) from the vessel as well asgaseous products of the reduction, in particular hydrogen and ammonia.Air is not a suitable purge gases as oxygen may result in decompositionof the hydrazine, which being an exothermic reaction can be potentiallyunsafe.

Unreacted hydrazine washed from the material after the reduction stepmay be disposed of according to known methods. It has been found that aparticularly suitable method of purifying this hydrazine containingaqueous waste stream is to catalytically decompose the hydrazine in theabsence of an oxidant over a suitable catalyst to nitrogen and ammonia.

Thus, according to a further aspect of the present invention there isprovided a process for the purification of a waste stream comprisingdilute aqueous hydrazine, which process comprises contacting the wastestream with a catalyst active for the decomposition of the hydrazine.Preferably, the catalyst active for the decomposition of hydrazinecomprises ruthenium on a support. The amount of ruthenium on the supportis preferably in the range from 1 to 10% by weight. Preferably, thesupport is selected from the group consisting of inorganic oxides suchas silica, alumina, zirconia and mixtures thereof as well as activatedcarbon and graphite. Preferably the reaction is performed attemperatures in the range from 0 to 100° C. by circulating the solutionthrough a fixed bed of catalyst. The residence time of the aqueoushydrazine solution within the catalyst bed should preferably becontrolled such that the temperature of the solution does not exceed itsboiling point, most preferably the solution temperature should bemaintained in the temperature range of 70 to 95° C.

In catalyst compositions suitable for the production of vinyl acetate,in addition to Group VIII noble metals such as palladium and optionalpromoter selected from gold, copper and cerium the support particles mayalso be impregnated with one or more salts of Group I, Group II,lanthanide and transition metals promoters, preferably of cadmium,barium, potassium, sodium, manganese, antimony, lanthanum or mixturesthereof, which are present in the finished catalyst composition assalts, typically acetates. Generally, potassium will be present.Suitable salts of these compounds are acetates but any soluble salt maybe used. These promoters may be used in an amount of 0.1 to 15%,preferably 3 to 9%, by weight of each promoter salt present in thefinished catalyst composition. It has been found that these promotersalts may be impregnated by blending support particles with solid saltsof the promoter metal in the presence of limited amount of solvent.

Thus, according to a further aspect of the present invention there isprovided a process for impregnating porous microspheroidal particleswith one or more salts of Group I, Group II, lanthanide and transitionmetals which process comprises blending the particles with one or moresolid salts of Group I, Group II, lanthanide and transition metals inthe presence of a solvent for the salt in which the solvent is containedwithin the pore volume of the catalyst support particle. Preferably thesolvent is water.

It has been found that by using a solid salt and catalyst particlescontaining a limited amount of solvent within the pore volume, the saltis impregnated within the support with a uniform distribution and may beperformed using the wet filtered material without the need of dryingprior to impregnation with a solution of the salt. Additionally,impregnation of the salt may be performed by blending the wet supportwith the solid salt in a blender (e.g. ribbon, V-type, ploughshare)which has an advantage that the same apparatus may be used for thesubsequent drying of the material.

Preferably, the support impregnated with one or more salts of Group I,Group II, lanthanide and transition metals is dried at a temperature inthe range from 60° C. to 150° C.

EXAMPLES

The invention will now be described by reference to the followingExamples.

Example 1

Preparation of WD-1.

Silica support (231.75 kg) was impregnated with an aqueous solution ofNa₂PdCl₄ (containing 4.10 kg palladium) and HAuCl₄ (containing 1.65 kggold) by the incipient wetness technique. The metal salts were dissolvedin demineralised water to give an impregnation solution of 124 liters(about 82% of the pore volume of the support particles). Theimpregnation was performed in a ribbon blender manufactured fromHastalloy C276 alloy.

Thereafter, the material was dried in the ribbon blender by introducingsteam into the steam jacket of the blender at a mean wall temperature of145° C. During the drying, a dry air purge was passed through theblender over the agitated material to remove the evolved moisture.

Thereafter the dried material was cooled to room temperature and theimpregnated salts were reduced to metallic state by addition of thesolid material to a stirred aqueous solution of hydrazine (946 liters,5% by weight hydrazine). The resultant slurry was allowed to standovernight with occasional stirring.

Thereafter, the material was decant washed 4 times with about 800 litersdemineralised water in each wash and dewatered using a rotating bowlcentrifuge.

The wet material (cake) was blended with solid anhydrous potassiumacetate (10 kg) in a ribbon blender and thereafter dried under agitationby introducing steam into the steam jacket of the blender to give a meanwall temperature of 145° C. The evolved moisture was removed with a dryair purge through the blender.

The resulting product was a free-flowing catalyst material suitable forfluid bed acetoxylation of ethylene to produce vinyl acetate.

Example 2

Preparation of 1.3R410.

Silica support (1124 kg) was impregnated with an aqueous solution ofNa₂PdCl₄ (containing 11.40 kg palladium) and HAuCl₄ (containing 4.56 kggold) by the incipient wetness technique. The metal salts were dissolvedin demineralised water to give an impregnation solution of 600 liters.The impregnation was performed in a ribbon blender manufactured fromHastalloy C276 alloy.

Thereafter, the material was dried in the ribbon blender by introducingsteam into the steam jacket of the blender to give a mean walltemperature of 120° C. During the drying, a dry air purge was passedthrough the blender over the agitated material to remove the evolvedmoisture.

The dried material was cooled to less than 35° C., initially by naturalcooling after isolation of the steam supply and thereafter byintroducing cooling water into the steam jacket.

Then the impregnated salts were reduced to metallic state by addition ofthe solid material to a stirred aqueous solution of hydrazine (2200liters, 5 % by weight hydrazine).

Thereafter, the material was then pumped to a Nutsche pressure filterand filtered under nitrogen. The filter cake was washed 3 times withabout 1000 liters of demineralised water in each wash.

The wet material (filter cake) was blended with solid anhydrouspotassium acetate (60 kg) in a ribbon blender and thereafter dried underagitation by introducing steam into the steam jacket of the blender togive a mean wall temperature of 120° C. The evolved moisture was removedwith a dry air purge through the blender. Drying was stopped when themoisture content of the material was in the range 20 to 25% by weight.The partially dried material was transferred to a fluid bed drieroperated at an air inlet temperature of 150° C. to remove the remainingmoisture.

The resulting product was a free-flowing catalyst material suitable forfluid bed acetoxylation of ethylene to produce vinyl acetate.

Example 3

Hydrazine Removal by Anaerobic Decomposition Over Ru/Silica

An aqueous hydrazine solution (2400 liters with [N2H4]=1.8 g/l) at atemperature of 66° C. was recirculated through a fixed bed of 2.6%Ru/silica catalyst (Johnson Matthey Type 660) containing 20 Kg catalyst.The flow rate through the catalyst bed was 2.21/min. Decomposition ofthe hydrazine was accompanied by evolution of gaseous products (N2, H2and NH3) and an increase in the temperature of the solution to 70° C.The solution was recirculated through the catalyst bed for a period of12 hours. Analysis of the final solution indicated that completedecomposition of the hydrazine had occurred ([N2H4]=<0.1 g/l,[NH4OH]=2.5 g/l).

Example 4

Hydrazine Decomposition Over a Range of Supported Ru Catalysts

An aqueous hydrazine solution (2.5 liters, [N2H4]=3.8% w/v) wasrecirculated through a flooded bed of Ru catalyst (catalyst bed volumetypically 500 ml) at a flow rate through the catalyst bed of 130 ml/min.Samples of the solution (1 to 5 ml) were removed at regular timeintervals and the concentration of hydrazine was determined. The resultsare summarised below

Catalyst Mass/ Solution % [N2H4] after Recirculation Times (min) gTemp/° C. 0 10 30 50 70 2.5% Ru/SiO2- 230 50 3.80 2.03 0.55 0.15 0.00Al2O3 2.5% Ru/SiO2 200 50 3.80 1.94 0.32 0.05 0.00 2.5% Ru/C 30 3.801.72 0.36 0.00 0.00

1. A process for preparing a catalyst active for the fluid bed acetoxylation of ethylene to produce vinyl acetate, which process comprises the steps of: (a) impregnating microspheroidal silica support particles by the incipient wetness technique with an aqueous solution of palladium and gold compounds, whilst agitating the support particles; (b) drying the impregnated support particles produced in step (a) whilst agitating the impregnated support particles; (c) reducing the palladium and gold compounds of the impregnated support particles produced in step (b) to respective metals by adding the dried, impregnated support particles to an aqueous solution of hydrazine, whilst stirring, to form a slurry; (d) filtering the slurry produced in step (c) to remove the excess reduction solution; (e) washing the filter cake/slurry produced in step (d) with water and removing excess water to form a cake; (f) impregnating the cake produced in step (e) with one or more salts of Group I, Group II, lanthanide and transition metals by blending the cake produced in step (e) with one or more solid salts of Group I, Group II, lanthanide and transition metals; and (g) drying the impregnated cake produced in step (f) whilst agitating the impregnated cake to form free-flowing catalyst particles.
 2. A process according to claim 1, wherein in step (a) the microspheroidal silica support particles are impregnated by the incipient wetness technique whilst continuously agitating the support particles.
 3. A process according to claim 1 in which the palladium compound is selected from the group consisting of palladium acetate, sulphate, nitrate, chloride, halogen-containing palladium compounds and Group I and Group II salts of halogen-containing palladium compounds.
 4. A process according to claim 1 wherein the gold compound is selected from the group consisting of gold chloride, dimethyl gold acetate, barium acetoaurate, gold acetate, tetrachloroauric acid and Group I and II salts of tetrachloroauric acid.
 5. A process according to claim 1 in which step (b) comprises agitating the impregnated support particles whilst applying external heat at a temperature in the range 50 to 200° C.
 6. A process according to claim 1 wherein in step (g) the cake is dried at a temperature in the range from 60 to 150° C.
 7. A process according to claim 1 in which the microspheroidal support particles are selected from the group consisting of silica, alumina, zirconia and mixtures thereof.
 8. A process as according to claim 1 in which step (a) and step (b) are performed in the same apparatus, said apparatus comprising a vessel being capable of being heated and agitated simultaneously.
 9. A process according to claim 8 wherein step (a) and step (b) are performed in an agitated blender.
 10. A process according to 1 in which step (f) and step (g) are performed in the same apparatus, said apparatus comprising a blender.
 11. A process according to claim 1 wherein the concentration of hydrazine in the aqueous solution is 1 to 20 wt %.
 12. A process according to claim 11 wherein the concentration of hydrazine is 3 to 20 wt %.
 13. A process according to claim 1 wherein the aqueous solution of hydrazine has not been rendered alkaline by an alkali metal hydroxide.
 14. A process according to claim 1 comprising preparing a catalyst containing at least about 0.1 wt % to about 5 wt % palladium and about 0.1 to about 3 wt % gold.
 15. A process according to claim 1 in which unreacted hydrazine washed from the material after the reduction step is decomposed in the absence of an oxidant over a supported ruthenium catalyst to nitrogen and ammonia.
 16. A process for impregnating microspheroidal catalyst support particles with at least one compound of a catalytically active group VIII noble metal, which process comprises the steps of: (a′) impregnating the microspheroidal support particles by the incipient wetness technique with an aqueous solution of the at least one catalytically active group VIII noble metal, whilst agitating the support particles; and (b′) drying the impregnated support particles produced in step (a′) whilst agitating the impregnated support particles; wherein steps (a′) and (b′) are performed in the same apparatus, said apparatus comprising an agitated blender.
 17. A process according to claim 16 in which step (b′) comprises agitating the impregnated support particles whilst applying external heat at a temperature in the range 50 to 200° C.
 18. A process according to claim 16 in which the microspheroidal support particles are selected from the group consisting of silica, alumina, zirconia and mixtures thereof.
 19. A process according to claim 16 in which the at least one catalytically active group VIII noble metal comprises palladium.
 20. A process according to claim 16 further comprising a step (c′), which comprises, contacting the impregnated support particles with a reducing agent to convert the at least one compound to its respective metal.
 21. A process according to claim 20 wherein the impregnated support particles are added to a solution of a reducing agent active for reduction of the at least one metal compound to its respective metal whilst stirring.
 22. A process according to claim 20 wherein the reducing agent comprises an aqueous solution of hydrazine.
 23. A process according to claim 22 wherein the concentration of hydrazine in the aqueous solution is 1 to 20 wt %.
 24. A process according to claim 23 wherein the concentration of hydrazine is 3 to 20 wt %.
 25. A process according to claim 20 further comprising a step (d′) wherein the support particles are further impregnated with one or more salts of Group I, Group II, lanthanide and transition metals, by blending the particles with one or more solid salts of Group I, Group II, lanthanide and transition metals in the presence of a solvent for the salt in which the solvent is contained within the pore volume of the catalyst support particle.
 26. A process according to claim 25 wherein the solvent is water.
 27. A process according to claim 25 which further comprises a step (e′) wherein the impregnated particles are dried at a temperature in the range from 60° C. to 150° C.
 28. A process according to claim 16 in which the at least one compound of a catalytically active metal impregnated in the support comprises palladium and gold compounds.
 29. A process for impregnating porous microspheroidal particles with one or more salts of Group I, Group II, lanthanide and transition metals which process comprises blending the particles with one or more solid salts of Group I, Group II, lanthanide and transition metals in the presence of a solvent for the salt in which the solvent is contained within the pore volume of the support particle.
 30. A process according to claim 29 wherein the solvent is water.
 31. A process according to claim 29 which further comprises the step of drying the impregnated particles at a temperature in the range from 60° C. to 150° C.
 32. A process according to claim 29 wherein the blending is performed in a blender.
 33. A process according to claim 29 in which the microspheroidal support particles are selected from the group consisting of silica, alumina, zirconia and mixtures thereof. 